The most common types of containers that are used for the pressure dispensing of fluids are of three types as follows:
1. The aerosol containers in which the pressure is provided for by means of a fluid that is liquid when under pressure and becomes a gas when the pressure is reduced.
2. Plastic containers, made of flexible material, that are pressurized when squeezed.
3. Containers for which the pressure for dispensing is provided by a pump.
All of the above types of containers have certain disadvantages.
The aerosol types of containers are pressurized by gases that are environmentally and fire hazardous, also the pressure must be high enough that the pressurizing medium will be kept in a liquid state while in the container and therefor when the dispensed material comes out of the container nozzle it either sprays or is squirted.
The squeeze type of container has the disadvantage that when it is partly empty and is inverted for dispensing and the material to be dispensed is somewhat viscous, it is necessary to wait for the material to flow by gravity down to the nozzle and for instance if the material is catsup or mustard the wait can be irritatingly slow and sometimes if the timing of the squeeze is not right a spattering occurs as air becomes trapped in the material.
Pumping containers have many small parts and are expensive to manufacture.
Many of the valves that are in service at present have small passageways between the valve seat and the atmosphere and these passageways retain material that can dry out or congeal and perhaps become contaminated with dirt or bacteria.
Most of the valves presently being used require some muscular effort to operate them and this may cause some problems for elderly people who are weak or for people that have arthritic problems in their hands.